The present invention relates to a fuel pump driving apparatus for a vehicle.
A fuel pump driving apparatus used in, e.g., a vehicle must be housed in a limited space of the vehicle. Therefore, it is important to decrease the number of components and the size of such a driving apparatus.
A conventional fuel pump driving apparatus FPD for a vehicle has an arrangement shown in FIG. 1, i.e., is constituted by a fuel pump control circuit 4 and a blocking oscillator 5 incorporated in a fuel pump. Referring to FIG. 1, reference symbol E denotes a battery; and F, a fuse. In addition, reference numeral 1 denotes an ignition switch; 2, an ignition coil having a primary winding and a secondary winding connected to an ignition plug P; and 3, a point breaker connected in parallel with a capacitor 3a.
The blocking oscillator 5 comprises a bias resistor 7 for a transistor (npn type in this case), a signal coil 8, an excitation coil or a main coil 9 for driving a fuel pump, diodes 10 to 12, and a surge absorber 13 for protecting a transistor 6 from a surge. Blocking oscillation is performed by electromagnetic coupling of the signal and main coils 8 and 9.
The fuel pump control circuit 4 includes a wave shaping circuit WFT connected to a node N1 between the point breaker 3 and the primary side of the ignition coil 2 through a terminal T4, a one-shot circuit OC connected to the output side of the wave shaping circuit WFT, a transistor TR to be ON/OFF-controlled by an output from the one-shot circuit OC, and a diode D. When an ignition pulse is supplied to the terminal T4, the transistor TR is kept On by the one-shot circuit OC for a predetermined time (t), and a power source on the terminal T1 side is connected to the blocking oscillator 5 through a terminal T2.
With the above-described arrangement, when a cam interlocked with the rotation of an engine is rotated, the point breaker 3 performs an ON/OFF operation. In accordance with this ON/OFF operation, a current is intermittently and periodically flowed in the primary winding of the ignition coil. A high voltage is generated in the secondary winding of the ignition coil 2 by an ignition pulse current based on a counter electromotive force which is generated in the primary winding of the ignition coil when the point breaker 3 is turned off. The high voltage is then applied to the ignition plug P.
At this time, an ignition pulse is generated at the primary side of the ignition coil 2, i.e., the node N1 between the coil 2 and the point breaker 3 when the current flowing through the primary side of the ignition coil 2 is OFF. This pulse is then supplied to the wave shaping circuit WFT of the fuel pump control circuit 4 through a terminal T4. The pulse is wave-shaped by the circuit WFT and is supplied to the one-shot circuit OC. The one-shot circuit OC is triggered at the trailing edge of the ignition pulse and keeps supplying an output to the input terminal of the transistor TR for a predetermined time (t) to turn on the transistor TR. As a result, the battery E is connected to the blocking oscillator 5 to cause the battery E to supply power to the oscillator 5. The blocking oscillator 5 is then oscillated to drive the fuel pump.
FIG. 2 shows a fuel pump assembly. The assembly is constituted by a fuel pump and the blocking oscillator 5. Since each component is known, a detailed description thereof will be omitted. Referring to FIG. 2, reference numeral 31 denotes a case main body; 32, a cover which is combined with the main body 31 to constitute an envelope; 34, a sleeve; 35 and 36, magnetic tubes; 37, a seal ring; 40, a coil bobbin around which the signal and main coils 8 and 9 are wound; 41, a printed board on which electric components are mounted; 42, a holder; 45 and 46, valves; 48, a plunger; 49, a coil spring; 51, a seal ring; and 53, a grommet. The components of the blocking oscillator 5 are mounted on the printed board 41.
A conventional fuel pump assembly has the above-described arrangement. If it is possible, the fuel pump control circuit 4 is preferably incorporated in the case main body 31. As described above, however, the fuel pump control circuit 4 includes the wave shaping circuit WFT and the one-shot circuit OC. These circuits, as is known, are constituted by several tens of electric components (e.g., resistors, transistors, capacitors, Zener diodes, and diodes). It is impossible to mount the fuel pump control circuit 4 on the above-described printed board together with the blocking oscillator 5. For this reason, the fuel pump control circuit 4 is formed separately of the fuel pump assembly. Therefore, a space for mounting the fuel pump control circuit is required, and the cost for mounting the control circuit in a vehicle is inevitably increased in addition to the cost of parts for attaching it to the vehicle. In addition, since the fuel pump and the fuel pump control circuit must be connected by wiring, reliability in connection of wiring must be taken into consideration.